Cardiac Cx43, Cx40 and Cx45 co-assembling: involvement of connexins epitopes in formation of hemichannels and Gap junction channels

Cx31.1 can selectively intermix with co-expressed connexins to facilitate its assembly into gap junctions

Connexins are channel-forming proteins that function to facilitate gap junctional intercellular communication. Here, we use dual cell voltage clamp and dye transfer studies to corroborate past findings showing that Cx31.1 (encoded by GJB5) is defective in gap junction channel formation, illustrating that Cx31.1 alone does not form functional gap junction channels in connexin-deficient mammalian cells. Rather Cx31.1 transiently localizes to the secretory pathway with a subpopulation reaching the cell surface, which is rarely seen in puncta reminiscent of gap junctions. Intracellular retained Cx31.1 was subject to degradation as Cx31.1 accumulated in the presence of proteasomal inhibition, had a faster turnover when Cx43 was present and ultimately reached lysosomes. Although intracellularly retained Cx31.1 was found to interact with Cx43, this interaction did not rescue its delivery to the cell surface. Conversely, the co-expression of Cx31 dramatically rescued the assembly of Cx31.1 into gap junctions where gap junction-mediated dye transfer was enhanced. Collectively, our results indicate that the localization and functional status of Cx31.1 is altered through selective interplay with co-expressed connexins, perhaps suggesting Cx31.1 is a key regulator of intercellular signaling in keratinocytes.

The intercalated disc: a unique organelle for electromechanical synchrony in cardiomyocytes

The intercalated disc (ID) is a highly specialized structure that connects cardiomyocytes via mechanical and electrical junctions. Although described in some detail by light microscopy in the 19th century, it was in 1966 that electron microscopy images showed that the ID represented apposing cell borders and provided detailed insight into the complex ID nanostructure. Since then, much has been learned about the ID and its molecular composition, and it has become evident that a large number of proteins, not all of them involved in direct cell-to-cell coupling via mechanical or gap junctions, reside at the ID. Furthermore, an increasing number of functional interactions between ID components are emerging, leading to the concept that the ID is not the sum of isolated molecular silos but an interacting molecular complex, an "organelle" where components work in concert to bring about electrical and mechanical synchrony. The aim of the present review is to give a short historical account of the ID's discovery and an updated overview of its composition and organization, followed by a discussion of the physiological implications of the ID architecture and the local intermolecular interactions. The latter will focus on both the importance of normal conduction of cardiac action potentials as well as the impact on the pathophysiology of arrhythmias.

Reprogramming of connexin landscape fosters fast gap junction intercellular communication in human papillomavirus-infected epithelia

Human papillomaviruses (HPVs) are highly prevalent commensal viruses that require epithelial stratification to complete their replicative cycle. While HPV infections are most often asymptomatic, certain HPV types can cause lesions, that are usually benign. In rare cases, these infections may progress to non-replicative viral cycles associated with high HPV oncogene expression promoting cell transformation, and eventually cancer when not cleared by host responses. While the consequences of HPV-induced transformation on keratinocytes have been extensively explored, the impact of viral replication on epithelial homeostasis remains largely unexplored. Gap junction intercellular communication (GJIC) is critical for stratified epithelium integrity and function. This process is ensured by a family of proteins named connexins (Cxs), including 8 isoforms that are expressed in stratified squamous epithelia. GJIC was reported to be impaired in HPV-transformed cells, which was attributed to the decreased expression of the Cx43 isoform. However, it remains unknown whether and how HPV replication might impact on the expression of Cx isoforms and GJIC in stratified squamous epithelia. To address this question, we have used 3D-epithelial cell cultures (3D-EpCs), the only model supporting the productive HPV life cycle. We report a transcriptional downregulation of most epithelial Cx isoforms except Cx45 in HPV-replicating epithelia. At the protein level, HPV replication results in a reduction of Cx43 expression while that of Cx45 increases and displays a topological shift toward the cell membrane. To quantify GJIC, we pioneered quantitative gap-fluorescence loss in photobleaching (FLIP) assay in 3D-EpCs, which allowed us to show that the reprogramming of Cx landscape in response to HPV replication translates into accelerated GJIC in living epithelia. Supporting the pathophysiological relevance of our observations, the HPV-associated Cx43 and Cx45 expression pattern was confirmed in human cervical biopsies harboring HPV. In conclusion, the reprogramming of Cx expression and distribution in HPV-replicating epithelia fosters accelerated GJIC, which may participate in epithelial homeostasis and host immunosurveillance.

Optogenetic termination of atrial tachyarrhythmias by brief pulsed light stimulation

AIMS

The most efficient way to acutely restore sinus rhythm from atrial fibrillation (AF) is electrical cardioversion, which is painful without adequate sedation. Recent studies in various experimental models have indicated that optogenetic termination of AF using light-gated ion channels may provide a myocardium-specific and potentially painless alternative future therapy. However, its underlying mechanism(s) remain(s) incompletely understood. As brief pulsed light stimulation, even without global illumination, can achieve optogenetic AF termination, besides direct conduction block also modulation of action potential (AP) properties may be involved in the termination mechanism. We studied the relationship between optogenetic AP duration (APD) and effective refractory period (ERP) prolongation by brief pulsed light stimulation and termination of atrial tachyarrhythmia (AT).

METHODS AND RESULTS

Hearts from transgenic mice expressing the H134R variant of channelrhodopsin-2 in atrial myocytes were explanted and perfused retrogradely. AT induced by electrical stimulation was terminated by brief pulsed blue light stimulation (470 nm, 10 ms, 16 mW/mm²) with 68% efficacy. The termination rate was dependent on pulse duration and light intensity. Optogenetically imposed APD and ERP changes were systematically examined and optically monitored. Brief pulsed light stimulation (10 ms, 6 mW/mm²) consistently prolonged APD and ERP when light was applied at different phases of the cardiac action potential. Optical tracing showed light-induced APD prolongation during the termination of AT.

CONCLUSION

Our results directly demonstrate that cationic channelrhodopsin activation by brief pulsed light stimulation prolongs the atrial refractory period suggesting that this is one of the key mechanisms of optogenetic termination of AT.

Cardiac Electrophysiological Changes and Downregulated Connexin 43 Prompts Reperfusion Arrhythmias Induced by Hypothermic Ischemia-Reperfusion Injury in Isolated Rat Hearts

The purpose of this study was to determine the utility of the monophasic action potential (MAP) changes as an arrhythmic biomarker in hypothermic ischemia-reperfusion. The hypothermic ischemia-reperfusion model was subjected to 60 min of cardioplegic arrest while the isolated rat hearts were preserved with a multidose cold K-H solution at 4 °C. During the reperfusion period, the heart's arrhythmia and monophasic action potential were also monitored. The myocardial damage was assessed using HE and TTC stains. Immunohistochemistry and Western blotting were used to assess the expression and distribution of Connexin 43 (Cx43) and Akt. Collectively, prolonged action potential durations, increased dispersion of repolarization, and downregulated and lateralized Cx43 all contribute to the derangement of electrical impulse propagation that may underlie arrhythmogenesis in the cold ischemic heart following cardioplegic arrest. MAP might be used as a biomarker for arrhythmias caused by hypothermic ischemia-reperfusion.

Zika Virus Infection Downregulates Connexin 43, Disrupts the Cardiomyocyte Gap Junctions and Induces Heart Diseases in A129 Mice

Zika virus (ZIKV) is transmitted mostly via mosquito bites and no vaccine is available, so it may reemerge. We and others previously demonstrated that neonatal infection of ZIKV results in heart failure and can be fatal. Animal models implicated ZIKV involvement in viral heart diseases. It is unknown whether and how ZIKV causes heart failure in adults. Herein, we studied the effects of ZIKV infection on the heart function of adult A129 mice. First, we found that ZIKV productively infects the rat-, mouse-, or human-originated heart cell lines and caused ubiquitination-mediated degradation of and distortive effects on connexin 43 (Cx43) protein that is important for communications between cardiomyocytes. Second, ZIKV infection caused 100% death of the A129 mice with decreasing body weight, worsening health score, shrugging fur, and paralysis. The viral replication was detected in multiple organs. In searching for the viral effects on heart of the A129 mice, we found that ZIKV infection resulted in the increase of cardiac muscle enzymes, implicating a viral acute myocardial injury. ZIKV-caused heart injury was also demonstrated by electrocardiogram (ECG) showing widened and fragmented QRS waves, prolonged PR interval, and slower heart rate. The intercalated disc (ICD) between two cardiomyocytes was destroyed, as shown by the electronic microscopy, and the Cx43 distribution in the ICDs was less organized in the ZIKV-infected mice compared to that in the phosphate-buffered saline (PBS)-treated mice. Consistently, ZIKV productively infected the heart of A129 mice and decreased Cx43 protein. Therefore, we demonstrated that ZIKV infection caused heart failure, which might lead to fatal sequelae in ZIKV-infected A129 mice. IMPORTANCE Zika virus (ZIKV) is a teratogen causing devastating sequelae to the newborns who suffer a congenital ZIKV infection while it brings about only mild symptoms to the health-competent older children or adults. Mouse models have played an important role in mechanistic and pathogenic studies of ZIKV. In this study, we employed 3 to 4 week-old A129 mice for ZIKV infection. RT-qPCR assays discovered that ZIKV replicated in multiple organs, including the heart. As a result of ZIKV infection, the A129 mice experienced weight loss, health score worsening, paralysis, and deaths. We revealed that the ZIKV infection caused abnormal electrocardiogram presentations, increased cardiac muscle enzymes, downregulated Cx43, and destroyed the gap junction and the intercalated disc between the cardiomyocytes, implicating that ZIKV may cause an acute myocardial injury in A129 mice. Therefore, our data imply that ZIKV infection may jeopardize the immunocompromised population with a severe clinical consequence, such as heart defect.

The caspase-1 inhibitor VX765 upregulates connexin 43 expression and improves cell-cell communication after myocardial infarction via suppressing the IL-1β/p38 MAPK pathway

Connexin 43 (Cx43) is the most important protein in the gap junction channel between cardiomyocytes. Abnormalities of Cx43 change the conduction velocity and direction of cardiomyocytes, leading to reentry and conduction block of the myocardium, thereby causing arrhythmia. It has been shown that IL-1β reduces the expression of Cx43 in astrocytes and cardiomyocytes in vitro. However, whether caspase-1 and IL-1β affect connexin 43 after myocardial infarction (MI) is uncertain. In this study we investigated the effects of VX765, a caspase-1 inhibitor, on the expression of Cx43 and cell-to-cell communication after MI. Rats were treated with VX765 (16 mg/kg, i.v.) 1 h before the left anterior descending artery (LAD) ligation, and then once daily for 7 days. The ischemic heart was collected for histochemical analysis and Western blot analysis. We showed that VX765 treatment significantly decreased the infarct area, and alleviated cardiac dysfunction and remodeling by suppressing the NLRP3 inflammasome/caspase-1/IL-1β expression in the heart after MI. In addition, VX765 treatment markedly raised Cx43 levels in the heart after MI. In vitro experiments were conducted in rat cardiac myocytes (RCMs) stimulated with the supernatant from LPS/ATP-treated rat cardiac fibroblasts (RCFs). Pretreatment of the RCFs with VX765 (25 μM) reversed the downregulation of Cx43 expression in RCMs and significantly improved intercellular communication detected using a scrape-loading/dye transfer assay. We revealed that VX765 suppressed the activation of p38 MAPK signaling in the heart tissue after MI as well as in RCMs stimulated with the supernatant from LPS/ATP-treated RCFs. Taken together, these data show that the caspase-1 inhibitor VX765 upregulates Cx43 expression and improves cell-to-cell communication in rat heart after MI via suppressing the IL-1β/p38 MAPK pathway.

PDGF-AA promotes gap junction intercellular communication in chondrocytes via the PI3K/Akt pathway

BACKGROUND

Gap junction intercellular communication (GJIC) plays an important role in cell growth, development and homeostasis. Connexin 43 (Cx43) is an important half-channel protein responsible for gap junction formation. Platelet-derived growth factor AA (PDGF-AA) regulates the proliferation, migration, metabolism, apoptosis and cell cycle of chondrocytes. However, the role of PDGF-AA in gap junction intercellular communication in chondrocytes is not fully understood. In the current study, we performed experiments to explore the effect of PDGF-AA on GJIC and its underlying biomechanical mechanism.

METHODS

qPCR was performed to determine the expression of PDGF, PDGFR and connexin family genes in chondrocytes and/or cartilage. A scrape loading/dye transfer assay was used to determine GJIC. Western blot analysis was applied to detect the expression of Cx43 and PI3K/Akt signaling pathway proteins. Immunofluorescence staining was utilized to examine protein distribution. Scanning electron microscopy was used to delineate the morphology of chondrocytes.

RESULTS

Expression of PDGF-A mRNA was highest among the PDGF family in chondrocytes and cartilage tissues. PDGF-AA promoted functional GJIC formation in chondrocytes by upregulating the expression of Cx43. Enhanced functional GJIC formation in chondrocytes induced by PDGF-AA occurred through the activation of PI3K/Akt signaling and its nuclear accumulation.

CONCLUSION

For the first time, this study provides evidence demonstrating the role of PDGF-AA in cell-to-cell communication in chondrocytes through mediating Cx43 expression.

Recombinant Adeno-Associated Viral Vector-Mediated Gene Transfer of hTBX18 Generates Pacemaker Cells from Ventricular Cardiomyocytes

Sinoatrial node dysfunction can manifest as bradycardia, leading to symptoms of syncope and sudden cardiac death. Electronic pacemakers are the current standard of care but are limited due to a lack of biological chronotropic control, cost of revision surgeries, and risk of lead- and device-related complications. We therefore aimed to develop a biological alternative to electronic devices by using a clinically relevant gene therapy vector to demonstrate conversion of cardiomyocytes into sinoatrial node-like cells in an in vitro context. Neonatal rat ventricular myocytes were transduced with recombinant adeno-associated virus vector 6 encoding either hTBX18 or green fluorescent protein and maintained for 3 weeks. At the endpoint, qPCR, Western blot analysis and immunocytochemistry were used to assess for reprogramming into pacemaker cells. Cell morphology and Arclight action potentials were imaged via confocal microscopy. Compared to GFP, hTBX18-transduced cells showed that hTBX18, HCN4 and Cx45 were upregulated. Cx43 was significantly downregulated, while sarcomeric α-actinin remained unchanged. Cardiomyocytes transduced with hTBX18 acquired the tapering morphology of native pacemaker cells, as compared to the block-like, striated appearance of ventricular cardiomyocytes. Analysis of the action potentials showed phase 4 depolarization and a significant decrease in the APD50 of the hTBX18-transduced cells. We have demonstrated that rAAV-hTBX18 gene transfer to ventricular myocytes results in morphological, molecular, physiological, and functional changes, recapitulating the pacemaker phenotype in an in vitro setting. The generation of these induced pacemaker-like cells using a clinically relevant vector opens new prospects for biological pacemaker development.

The Role of Gap Junctions in the Generation of Smooth Muscle Cells from Bone Marrow Mesenchymal Stem Cells

Background. Studies have shown that stem cell transplantation can improve smooth muscle cell (SMC) regeneration and remodelling. Gap junctions can enhance the cytoprotective effects of neighbouring cells. We investigated the effect of gap junctions on the differentiation of bone marrow mesenchymal stem cells (BMSCs) into SMCs. Materials and Methods. Rat BMSCs and SMCs were obtained from the bone marrow and bladder of Sprague-Dawley rats, respectively. Flow cytometry and multilineage differentiation were performed to assess the characteristics of these cells. BMSCs and SMCs were incubated together in cocultures in the presence and absence of heptanol, an uncoupler of gap junctions. Cocultures were divided into three groups consisting of a contact coculture, noncontact coculture, and contact coculture plus heptanol groups. The expression of BMSC-specific markers and the effect of gap junctions on the differentiation of BMSCs were evaluated by performing real-time reverse transcription-polymerase chain reaction, immunofluorescence analysis, and western blotting after cocultures. Results. CD90 and CD44 were markedly expressed, and CD31 and CD45 were weakly or not expressed in BMSCs. The cells also showed good osteogenic and adipogenic differentiation ability. Compared with the noncontact coculture group, the SMC markers such as α-SMA, calponin, and connexin43 increased in the contact coculture group. The effect of contact in the coculture group was significantly weakened by heptanol. Conclusions. The results suggested that gap junctions play an important role in the generation of SMCs from BMSCs. The formation of SMCs can potentially be used to repair the sphincter muscle of patients with stress urinary incontinence.

Gene therapy to terminate tachyarrhythmias

INTRODUCTION

To date, the treatment option for tachyarrhythmia is classified into drug therapy, catheter ablation, and implantable device therapy. However, the efficacy of the antiarrhythmic drugs is limited. Although the indication of catheter ablation is expanding, several fatal tachyarrhythmias are still refractory to ablation. Implantable cardioverter-defibrillator increases survival, but it is not a curable treatment. Therefore, a novel therapy for tachyarrhythmias refractory to present treatments is desired. Gene therapy is being developed as a promising candidate for this purpose, and basic research and translational research have been accumulated in recent years.

AREAS COVERED

This paper reviews the current state of gene therapy for arrhythmias, including susceptible arrhythmias, the route of administration to the heart, and the type of vector to use. We also discuss the latest progress in the technology of gene delivery and genome editing.

EXPERT OPINION

Gene therapy is one of the most promising technologies for arrhythmia treatment. However, additional technological innovation to achieve safe, localized, homogeneous, and long-lasting gene transfer is required for its clinical application.

Atrial Fibrillation: Focus on Myocardial Connexins and Gap Junctions

Atrial fibrillation (AF) represents the most common type of clinical cardiac arrhythmia worldwide and contributes to substantial morbidity, mortality and socioeconomic burden. Aggregating evidence highlights the strong genetic basis of AF. In addition to chromosomal abnormalities, pathogenic mutations in over 50 genes have been causally linked to AF, of which the majority encode ion channels, cardiac structural proteins, transcription factors and gap junction channels. In the heart, gap junctions comprised of connexins (Cxs) form intercellular pathways responsible for electrical coupling and rapid coordinated action potential propagation between adjacent cardiomyocytes. Among the 21 isoforms of connexins already identified in the mammal genomes, 5 isoforms (Cx37, Cx40, Cx43, Cx45 and Cx46) are expressed in human heart. Abnormal electrical coupling between cardiomyocytes caused by structural remodeling of gap junction channels (alterations in connexin distribution and protein levels) has been associated with enhanced susceptibility to AF and recent studies have revealed multiple causative mutations or polymorphisms in 4 isoforms of connexins predisposing to AF. In this review, an overview of the genetics of AF is made, with a focus on the roles of mutant myocardial connexins and gap junctions in the pathogenesis of AF, to underscore the hypothesis that cardiac connexins are a major molecular target in the management of AF.

Genomic and Non-Genomic Regulatory Mechanisms of the Cardiac Sodium Channel in Cardiac Arrhythmias

Nav1.5 is the predominant cardiac sodium channel subtype, encoded by the SCN5A gene, which is involved in the initiation and conduction of action potentials throughout the heart. Along its biosynthesis process, Nav1.5 undergoes strict genomic and non-genomic regulatory and quality control steps that allow only newly synthesized channels to reach their final membrane destination and carry out their electrophysiological role. These regulatory pathways are ensured by distinct interacting proteins that accompany the nascent Nav1.5 protein along with different subcellular organelles. Defects on a large number of these pathways have a tremendous impact on Nav1.5 functionality and are thus intimately linked to cardiac arrhythmias. In the present review, we provide current state-of-the-art information on the molecular events that regulate SCN5A/Nav1.5 and the cardiac channelopathies associated with defects in these pathways.

ERGIC2 and ERGIC3 regulate the ER-to-Golgi transport of gap junction proteins in metazoans

The extremely dynamic life cycle of gap junction connections requires highly efficient intracellular trafficking system especially designed for gap junction proteins, but the underlying mechanisms are largely unknown. Here, we identified that the COPII-associated proteins ERGIC2 (ER-Golgi intermediate compartment) and ERGIC3 are specifically required for the efficient intracellular transport of gap junction proteins in both C. elegans and mice. In the absence of Ergic2 or Ergic3, gap junction proteins accumulate in the ER and Golgi apparatus and the size of endogenous gap junction plaques is reduced. Knocking out the Ergic2 or Ergic3 in mice results in heart enlargement and cardiac malfunction accompanied by reduced number and size of connexin 43 (Cx43) gap junctions. Invertebrates' gap junction protein innexins share no sequence similarity with vertebrates' connexins. However, ERGIC2 and ERGIC3 could bind to gap junction proteins in both worms and mice. Characterization of the highly specialized roles of ERGIC2 and ERGIC3 in metazoans reveals how the early secretory pathway could be adapted to facilitate the efficient transport for gap junction proteins in vivo. This article is protected by copyright. All rights reserved.

Abnormal Expression of Connexin43 in Cardiac Injury Induced by S-Band and X-Band Microwave Exposure in Rats

Although the effects of microwave exposure on the heart have gradually become the focus of domestic and foreign scholars, the biological effects caused by different doses and different frequency bands of exposure are still unclear. In this study, we will investigate the damaging effect of S-band and X-band microwave composite exposure on cardiac structure and function, as well as the pathophysiological significance of Cx43 in cardiac conduction dysfunction after exposure. We used S- and X-band radiation sources with the average power density of 5 and 10 mW/cm² to expose Wistar rats to single or composite exposure. At the 6^th hour, on the 7^th, 14^th, and 28^th days after exposure, ECG was used to detect the electrical conduction of the heart, and the myocardial enzyme was measured by the automatic biochemical analyzer. We selected the observation time points and groups with severe damage to observe the changes of myocardial structure and ultrastructure with an optical microscope and TEM; and to detect the expression and distribution of Cx43 by western blotting and immunohistochemistry. After exposure, the heart rate increased, the P wave amplitude decreased, and the R wave amplitude increased; the content of the myocardial enzyme in serum increased; the structure and ultrastructure of cardiac tissue were damaged. The damage was dose-dependent and frequency-dependent. The expression of Cx43 in myocardial tissue decreased, and distribution was abnormal. Taken together, these findings suggested that the mechanism of abnormal electrical conduction in the heart of rats by S- and X-band microwave exposure might be related to the decreased expression and disordered distribution of Cx43 after microwave exposure.

A possible follow-up method for diabetic heart failure patients

INTRODUCTION

Plasma osmolarity is maintained through various mechanisms. The osmolarity of the aqueous humor around the crystalline lens is correlated with plasma osmolarity. A vacuole can be formed in the lens upon changes in osmolarity. The sodium-glucose cotransporter 2 inhibitors (SGLT2i) are new in the treatment of heart failure. They can cause osmotic diuresis but do not affect plasma osmolarity.

OBJECTIVE

It is unclear if the presence or absence of lens vacuole changes can monitor diabetic heart failure and SGLT2i treatment efficacy.

METHODS

Web of Science, PubMed and Scopus databases were searched for relevant articles about osmolarity, diabetes, transient receptor potential vanilloid channel, diabetic heart failure, lens vacuoles up to May 2021.

MAIN MESSAGE

The effect of SGLT2i on osmosis underlies its benefit to heart failure, but this in turn affects many other mechanisms. Failure to experience osmolarity changes will reduce the negative changes in terms of heart failure affected by osmolarity. A practical observable method is needed.

CONCLUSIONS

There is a possibility of using lens vacuoles in the follow-up of diabetic heart failure patients.

Genetic basis and molecular biology of cardiac arrhythmias in cardiomyopathies

Cardiac arrhythmias are common, often the first, and sometimes the life-threatening manifestations of hereditary cardiomyopathies. Pathogenic variants in several genes known to cause hereditary cardiac arrhythmias have also been identified in the sporadic cases and small families with cardiomyopathies. These findings suggest a shared genetic aetiology of a subset of hereditary cardiomyopathies and cardiac arrhythmias. The concept of a shared genetic aetiology is in accord with the complex and exquisite interplays that exist between the ion currents and cardiac mechanical function. However, neither the causal role of cardiac arrhythmias genes in cardiomyopathies is well established nor the causal role of cardiomyopathy genes in arrhythmias. On the contrary, secondary changes in ion currents, such as post-translational modifications, are common and contributors to the pathogenesis of arrhythmias in cardiomyopathies through altering biophysical and functional properties of the ion channels. Moreover, structural changes, such as cardiac hypertrophy, dilatation, and fibrosis provide a pro-arrhythmic substrate in hereditary cardiomyopathies. Genetic basis and molecular biology of cardiac arrhythmias in hereditary cardiomyopathies are discussed.

Gap Junctional Communication via Connexin43 between Purkinje Fibers and Working Myocytes Explains the Epicardial Activation Pattern in the Postnatal Mouse Left Ventricle

The mammalian ventricular myocardium forms a functional syncytium due to flow of electrical current mediated in part by gap junctions localized within intercalated disks. The connexin (Cx) subunit of gap junctions have direct and indirect roles in conduction of electrical impulse from the cardiac pacemaker via the cardiac conduction system (CCS) to working myocytes. Cx43 is the dominant isoform in these channels. We have studied the distribution of Cx43 junctions between the CCS and working myocytes in a transgenic mouse model, which had the His-Purkinje portion of the CCS labeled with green fluorescence protein. The highest number of such connections was found in a region about one-third of ventricular length above the apex, and it correlated with the peak proportion of Purkinje fibers (PFs) to the ventricular myocardium. At this location, on the septal surface of the left ventricle, the insulated left bundle branch split into the uninsulated network of PFs that continued to the free wall anteriorly and posteriorly. The second peak of PF abundance was present in the ventricular apex. Epicardial activation maps correspondingly placed the site of the first activation in the apical region, while some hearts presented more highly located breakthrough sites. Taken together, these results increase our understanding of the physiological pattern of ventricular activation and its morphological underpinning through detailed CCS anatomy and distribution of its gap junctional coupling to the working myocardium.

p38 MAPK Pathway in the Heart: New Insights in Health and Disease

The p38 mitogen-activated kinase (MAPK) family controls cell adaptation to stress stimuli. p38 function has been studied in depth in relation to cardiac development and function. The first isoform demonstrated to play an important role in cardiac development was p38α; however, all p38 family members are now known to collaborate in different aspects of cardiomyocyte differentiation and growth. p38 family members have been proposed to have protective and deleterious actions in the stressed myocardium, with the outcome of their action in part dependent on the model system under study and the identity of the activated p38 family member. Most studies to date have been performed with inhibitors that are not isoform-specific, and, consequently, knowledge remains very limited about how the different p38s control cardiac physiology and respond to cardiac stress. In this review, we summarize the current understanding of the role of the p38 pathway in cardiac physiology and discuss recent advances in the field.

Network construction of aberrantly expressed miRNAs and their target mRNAs in ventricular myocardium with ischemia-reperfusion arrhythmias

Background

Hypothermic ischemia-reperfusion arrhythmia remains the main factor affecting cardiac resuscitation under cardiopulmonary bypass. Existing research shows that certain miRNAs exhibit significantly different expressions and effects in arrhythmias, however, the effect of miRNAs on the progression of hypothermic ischemic–reperfusion arrhythmias (RA) and its potential mechanism remain to be further explored.

Methods

Sprague-Dawley (SD) rats were randomly divided into two groups (n = 8): a normal control group (Group C) and a hypothermic ischemia-reperfusion group (Group IR), which were used to establish a Langendorff isolated cardiac perfusion model. According to the arrhythmia scoring system, rats in group IR were divided into a high-risk group (IR-H) and a low-risk group (IR-L). miRNAs expression profiles of ventricular myocardium with global hypothermic ischemia–reperfusion and those of ventricular myocardium with hypothermic ischemia–RA were established through high-throughput sequencing. Furthermore, the aberrantly expressed miRNAs in myocardium with and without hypothermic ischemia–RA were screened and verified. The target genes of these aberrantly expressed miRNAs were predicted using RNAhybrid and MiRanda software. Based on Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, we determined the mRNA targets associated with these miRNAs and studied the miRNA–mRNA interaction during the cardiovascular disease progression. The aberrantly expressed miRNAs related to hypothermic ischemia–RA were validated by Real-time Quantitative polymerase chain reaction (RT-qPCR).

Results

Eight significantly aberrantly expressed miRNAs (rno-miR-122-5p, rno-miR-429, novel_miR-1, novel_miR-16, novel_miR-17, novel_miR-19, novel_miR-30, and novel_miR-43) were identified, among which six were up-regulated and two were down-regulated. Moreover, target genes and signaling pathways associated with these aberrantly expressed miRNAs were predicted and analyzed. The miRNA–mRNA interaction network graph showed that GJA1 gene was considered as the target of novel_miR-17.

Conclusions

Aberrantly expressed miRNAs were possibly associated with the formation mechanism of hypothermic ischemia–RA. Specific miRNAs, such as novel_miR-17 and rno-miR-429 are probably new potential targets for further functional studies of hypothermic ischemia–RA.

Gene therapy for atrial fibrillation - How close to clinical implementation?

In this review we examine the current state of gene therapy for the treatment of cardiac arrhythmias. We describe advances and challenges in successfully creating and incorporating gene vectors into the myocardium. After summarizing the current scientific research in gene transfer technology we then focus on the most promising areas of gene therapy, the treatment of atrial fibrillation and ventricular tachyarrhythmias. We review the scientific literature to determine how gene therapy could potentially be used to treat patients with cardiac arrhythmias.

Theaflavin 3,3'-digallate reverses the downregulation of connexin 43 and autophagy induced by high glucose via AMPK activation in cardiomyocytes

Theaflavin 3,3'-digallate (TF3), is reported to protect cardiomyocytes from lipotoxicity and reperfusion injury. However, the role of TF3 in the protection of high-glucose injury is still poorly understood. This study investigated the protective effects of TF3 on gap junctions and autophagy in neonatal cardiomyocytes (NRCMs). NRCMs preincubated with high glucose were coincubated with TF3. The expression of connexins and autophagy-related proteins was determined. The functioning of gap-junctional intercellular communication (GJIC) was measured by a dye transfer assay. Adenosine monophosphate-activated protein kinase (AMPK) activity was determined by western blot. Moreover, AMPK was activated with aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) or inhibited by AMPKα small interfering RNA (siRNA) to explore the role of AMPK in the modulation of connexin 43 (Cx43) and autophagy. Meanwhile, autophagy was activated or blocked to observe the change in Cx43 expression. It was found that the protein expression of Cx43 and autophagy-related proteins was increased in a TF3 dose- and time-dependent manner under high glucose. TF3 also recovered the reduced GJIC function induced by high glucose concentrations. TF3 activated phosphorylated AMPK in a time-dependent way. AMPKα siRNA abrogated the protection of TF3, while AICAR showed similar results compared to the TF3 treatment. Meanwhile, autophagy activation caused decreased Cx43, while cotreatment with baf A1 enhanced Cx43 expression further compared with the TF3 treatment alone under high glucose. We concluded that TF3 partly reversed the inhibition of Cx43 expression and autophagy induced by high glucose in NRCMs, partly by restoring AMPK activity. Inhibition of autophagy might be protective by preserving Cx43 expression in NRCMs stimulated by high glucose.

MiR-301a-3p in the pathogenesis of bacterial meningitis by targeting Cx43

Gap junction (GJ) is concerned with cell growth, differentiation, immune response, as well as many physiological and pathological processes. Cx43, as an important GJ protein, is associated with a variety of diseases. This study investigated the effect of miR-301a-3p in bacterial meningitis by targeting the Cx43 gene. The negative correlation between Cx43 and miR-301a-3p was because of the abnormal expression of related genes. MiR-301a-3p agomir was transfected into astrocytes for higher expression; CCK8 assay and flow cytometry showed that the high expression of miR-301a-3p would inhibit apoptosis and induces proliferation of astrocytes, whereas miR-301a-3p antagomir would inhibit proliferation and induce apoptosis. Bioinformatics analysis showed that Cx43 was the target gene of miR-301a-3p, and dual-luciferase assay and experiments repeated showed that miR-301a-3p regulated the expression of Cx43 on the 3'-untranslated region seed region. Therefore, miR-301a-3p played a biological role in the development of bacterial meningitis by regulating the expression of the target gene Cx43.

Connexins and Atrial Fibrillation in Obstructive Sleep Apnea

PURPOSE OF THE REVIEW

To summarize the potential interactions between obstructive sleep apnea (OSA), atrial fibrillation (AF), and connexins.

RECENT FINDINGS

OSA is highly prevalent in patients with cardiovascular disease, and is associated with increased risk for end-organ substantial morbidities linked to autonomic nervous system imbalance, increased oxidative stress and inflammation, ultimately leading to reduced life expectancy. Epidemiological studies indicate that OSA is associated with increased incidence and progression of coronary heart disease, heart failure, stroke, as well as arrhythmias, particularly AF. Conversely, AF is very common among subjects referred for suspected OSA, and the prevalence of AF increases with OSA severity. The interrelationships between AF and OSA along with the well-known epidemiological links between these two conditions and obesity may reflect shared pathophysiological pathways, which may depend on the intercellular diffusion of signaling molecules into either the extracellular space or require cell-to-cell contact. Connexin signaling is accomplished via direct exchanges of cytosolic molecules between adjacent cells at gap membrane junctions for cell-to-cell coupling. The role of connexins in AF is now quite well established, but the impact of OSA on cardiac connexins has only recently begun to be investigated. Understanding the biology and regulatory mechanisms of connexins in OSA at the transcriptional, translational, and post-translational levels will undoubtedly require major efforts to decipher the breadth and complexity of connexin functions in OSA-induced AF.

SUMMARY

The risk of end-organ morbidities has initiated the search for circulating mechanistic biomarker signatures and the implementation of biomarker-based algorithms for precision-based diagnosis and risk assessment. Here we summarize recent findings in OSA as they relate to AF risk, and also review potential mechanisms linking OSA, AF and connexins.

Syncytium calcium signaling and macrophage function in the heart

Macrophages are traditionally viewed as a key component of the immunity defense system. Recent studies have identified resident macrophages in multiple organs including the heart, in which the cells perform their crucial role on tissue repair after myocardial infarction (MI). The cardiac-specific macrophages interdigitate with cardiomyocytes particularly at the atrioventricular node region. The integrative communication between macrophage and cardiomyocytes can modulate the contractile function of the heart. Coordinated control of intracellular calcium signaling and intercellular electrical conduction via the syncytium network underlie the synchronized beating of the heart. In this review article, we introduce the concept the syncytium calcium signaling in the cardiomyocytes can modulate gene expression in the resident macrophages and their integration with the cardiomyocytes. The cardiac macrophages originate from bone marrow stem cells, migrate to local via vessel, and settle down as a naturalization process in heart. As the macrophages perform on regulating electrical conduction, and accomplish post MI non-scared completed regeneration or partial regeneration with fibrotic scar at different stage of postnatal development, we understand that multiple functions of cardiac macrophage should carry on with diverse linages. The naturalization process in heart of macrophages to the cardiomyocytes serves important roles to control of electrical signaling and calcium-dependent contractile function of the heart.

Role of Non-Myocyte Gap Junctions and Connexin Hemichannels in Cardiovascular Health and Disease: Novel Therapeutic Targets?

The heart is a complex organ composed of multiple cell types, including cardiomyocytes and different non-myocyte populations, all working closely together to determine the hearts properties and maintain normal cardiac function. Connexins are abundantly expressed proteins that form plasma membrane hemichannels and gap junctions between cells. Gap junctions are intracellular channels that allow for communication between cells, and in the heart they play a crucial role in cardiac conduction by coupling adjacent cardiomyocytes. Connexins are expressed in both cardiomyocytes and non-myocytes, including cardiac fibroblasts, endothelial cells, and macrophages. Non-myocytes are the largest population of cells in the heart, and therefore it is important to consider what roles connexins, hemichannels, and gap junctions play in these cell types. The aim of this review is to provide insight into connexin-based signalling in non-myocytes during health and disease, and highlight how targeting these proteins could lead to the development of novel therapies. We conclude that connexins in non-myocytes contribute to arrhythmias and adverse ventricular remodelling following myocardial infarction, and are associated with the initiation and development of atherosclerosis. Therefore, therapeutic interventions targeting these connexins represent an exciting new research avenue with great potential.

miRNA Expression Profile and Effect of Wenxin Granule in Rats with Ligation-Induced Myocardial Infarction

Wenxin Granule (WXKL) is a traditional Chinese medicine used for treatment of myocardial infarction (MI) and arrhythmias. However, the genomic pathological mechanisms of MI and mechanisms of WXKL are largely unknown. This study aims to investigate a comprehensive miRNA expression profile, and the predicted correlation pathways to be targeted by differentially expressed miRNAs in MI, and mechanisms of WXKL from a gene level. MI rat model was established by a coronary artery ligation surgery. miRNA expression microarrays were performed and the data were deposited in Gene Expression Omnibus (GEO number GSE95855). And, pathway analysis was performed by using the DIANA-miRPath v3.0 online tool. The expressions of miR-1, miR-133, Cx43, and Cx45 were detected by quantitative real-time PCR. It was found that 35 differentially expressed miRNAs and 23 predicted pathways, including miR-1, miR-133, and gap junction pathway, are involved in the pathogenesis of MI. And, WXKL increased the expressions of miR-1 and miR-133, while also increased the mRNA levels of Cx43 and Cx45, and, especially, recovered the Cx43/Cx45 ratio near to normal level. The results suggest that regulatory effects on miR-1, miR-133, Cx43, and Cx45 might be a possible mechanism of WXKL in the treatment of MI at the gene level.

Cardiac Fibrosis and Arrhythmogenesis

Myocardial injury, mechanical stress, neurohormonal activation, inflammation, and/or aging all lead to cardiac remodeling, which is responsible for cardiac dysfunction and arrhythmogenesis. Of the key histological components of cardiac remodeling, fibrosis either in the form of interstitial, patchy, or dense scars, constitutes a key histological substrate of arrhythmias. Here we discuss current research findings focusing on the role of fibrosis, in arrhythmogenesis. Numerous studies have convincingly shown that patchy or interstitial fibrosis interferes with myocardial electrophysiology by slowing down action potential propagation, initiating reentry, promoting after-depolarizations, and increasing ectopic automaticity. Meanwhile, there has been increasing appreciation of direct involvement of myofibroblasts, the activated form of fibroblasts, in arrhythmogenesis. Myofibroblasts undergo phenotypic changes with expression of gap-junctions and ion channels thereby forming direct electrical coupling with cardiomyocytes, which potentially results in profound disturbances of electrophysiology. There is strong evidence that systemic and regional inflammatory processes contribute to fibrogenesis (i.e., structural remodeling) and dysfunction of ion channels and Ca2+ homeostasis (i.e., electrical remodeling). Recognizing the pivotal role of fibrosis in the arrhythmogenesis has promoted clinical research on characterizing fibrosis by means of cardiac imaging or fibrosis biomarkers for clinical stratification of patients at higher risk of lethal arrhythmia, as well as preclinical research on the development of antifibrotic therapies. At the end of this review, we discuss remaining key questions in this area and propose new research approaches. © 2017 American Physiological Society. Compr Physiol 7:1009-1049, 2017.

The cytoplasmic translocation of Cx32 mediates cisplatin resistance in ovarian cancer cells

Ovarian cancer is the most lethal gynecologic malignancy, and cisplatin is one of the first-line chemotherapeutic agents. However, acquired cisplatin resistance prevents the successful treatment of patients with ovarian cancer. Gap junction (GJ) and connexin (Cx) are closely related to tumor formation, but the relationship between cisplatin resistance and GJ or Cx are undetermined. In this study, we established the cisplatin-resistant human ovarian cancer cell line A2780-CDDP. Here we showed that cisplatin resistance was correlated to the loss of GJ and the upregulation of Cx32 expression. Enhancing GJ in A2780-CDDP cells could increase the apoptotic response to cisplatin treatment. Furthermore, although Cx32 expression was increased in A2780-CDDP cells, it was more localized to the cytoplasm rather than in the membrane, and knockdown of Cx32 in A2780-CDDP cells sensitized them to cisplatin treatment. In summary, Cx32 is involved in cisplatin resistance, and cytoplasmic Cx32 plays an important role in chemoresistance.